Charge transport processes at interfaces which are governed by complex interfacial electronic structure play a crucial role in catalytic reactions, energy storage, photovoltaics, and many biological processes. Here, the first soft X-ray second harmonic generation (SXR-SHG) interfacial spectrum of a buried interface (boron/Parylene-N)is reported. SXR-SHG shows distinct spectral features that are not observed in X-ray absorption spectra, demonstrating its extraordinary interfacial sensitivity. Comparison to electronic structure calculations indicates a boron-organic separation distance of 1.9±0.1 Å, wherein changes as small as 0.1 Å result in easily detectable SXR-SHG spectral shifts (ca. 100s of meV). As SXR-SHG is inherently ultrafast and sensitive to individual atomic layers, it creates the possibility to study a variety of interfacial processes, e.g. catalysis, with ultrafast time resolution and bond specificity.
This work was done in collaboration with researchers from the Saykally group at UCB, LBNL, UC San Diego, SLAC, and FERMI. The experiments were conducted at the free-electron laser facility FERMI in Italy.
Our paper was now published in Physical Review Letters:
In this work, we utilize XUV-SHG spectroscopy to investigate the polar metal phase of LiOsO3, where the coexistence of polarity and metallicity is unexpected since the itinerant conducting electrons in metals are expected to screen out long-range electrostatic forces that typically stabilize a permanent polarization. This is one of the first uses of nonlinear X-ray spectroscopy to investigate a material across a phase transition. A sensitivity to broken inversion symmetry appears above the Li K-edge, with theory showing how the spectrally-resolved SHG varies with Li-displacement. As the first demonstration of XUV-SHG spectroscopy around a phase transition, these results pave the way for using nonlinear XUV methods to investigate broken symmetry from an element-specific perspective.
Congratulations to Emma for her first author paper, and Angelique and Can for their first paper in the group. Also, we are excited for Clarisse’ first paper, who contributed to this work during her NSF-REU visit last summer.
This work was done in collaboration with researchers from LBNL, UC San Diego, Argonne National Laboratory, Penn State, and the University of Tokio. The experiments were conducted at the free-electron laser facility SACLA in Japan.
Our paper appeared in Nano Letters (open access) and was selected as cover featured article:
College of Chemistry news release:
We had our first retreat as a group and went hiking two days in Yosemite National Park. Giant Sequoias, Glacier Point and several waterfalls were explored. Despite 103 degrees, it has been a very memorable retreat.
Michael was awarded the 2021 Fresnel Prize by the European Physical Society – Quantum Electronics and Optics Division in the “fundamental research” category “for outstanding contributions to the field of ultrafast condensed-matter science and for the application of linear and nonlinear X-ray spectroscopies to the investigation of quantum phenomena“. The Fresnel Prize is awarded every 2 years to a researcher 35 years or younger, one each in the areas of fundamental and applied research. The award ceremony took place virtually during the CLEO Europe conference.
College of Chemistry News Release:
Nonlinear optical spectroscopies have significantly advanced the understanding of chemical dynamics at surfaces. One limitation in the optical regime has been the constrain to valence dynamics making probing in complex chemical environments and attributing dynamics to specific atomic species difficult. We now demonstrate second harmonic generation (SHG) on titanium in the extreme ultraviolet (XUV) using a femtosecond table-top laser. We show that the observed XUV-SHG emission is specific to the inversion-symmetry broken surface of titanium. These findings open new possibilities to study chemical dynamics at surfaces and buried interfaces from the viewport of a specific atomic species.
In collaboration with Institut Polytechnique de Paris, UC San Diego, SLAC National Accelerator Laboratory, and the Friedrich Schiller University Jena.
Congratulations to Emma for her first shared-first author paper and to Lars for his first paper in the group!
Our paper appeared in Science Advances and was selected as cover featured article:
Press release from the College of Chemistry:
We are so excited to welcome several new group members starting April and May 2021! Nadia Berndt joins us as an undergraduate researcher working on time-resolved spectroscopy on encapsulated monolayer TMDC nano discs. Finn Kohrell (Friedrich Schiller University Jena, Germany) is a visiting student researcher funded by the German Academic Exchange Service (DAAD) conducting research for his Master thesis on non-equilibrium dynamics in the superconducting state of 2D TMDCs at low temperatures for the next year. Sophia Fang (MIT) joins us for the summer as NSF-REU student and will work on attosecond pulse generation and dynamics. William Alexander is a freshman in Chemistry and Entrepreneurship and joins us as undergraduate researcher exploring new ways for applying virtual reality in lab instruction and laser lab operation. Last but not least, Douglas Heine (Michigan State University) joins us this summer as NSF-REU student working on simulating strong-field excitations in two-dimensional semiconductors.
We are happy to see Can’s first first-author manuscript submitted on polarization-resolved second harmonic spectroscopy enabling element-resolved angular anisotropy investigations. In LiNbO3 we directly resolve the Li ion displacement and its correlated action on the Nb-O bonds. This study constitutes the first observation of polarization-resolved SHG in the extreme ultraviolet (XUV) and we show that dipole-based SHG models used regularly in the optical regime allow predicting the SHG polarization in the in the XUV regime.
This work as performed at the SACLA free-electron laser at Sping8/RIKEN in primary collaboration with UC San Diego, Argonne National Lab, LBNL and U Tokyo.
Link to Arxiv manuscript:
Michael got appointed to the editorial board at Nanoscale Research Letters (NRL) at SpringerOpen which is part of Springer-Nature. NRL is a peer-reviewed open access journal focusing on nanoscale research in physics, materials science, biology, chemistry, and engineering.
We are so excited that Emma got awarded the NSF Graduate Fellowship. Hearthy congratulations!
Recent developments in attosecond technology led to table-top x-ray spectroscopy in the soft x-ray range, thus uniting the element- and state-specificity of core-level x-ray absorption spectroscopy with the time resolution to follow electronic dynamics in real-time. In this new paper we describe recent work in attosecond technology and investigations into materials such as Si, SiO2, GaN, Al2O3, Ti, and TiO2, enabled by the convergence of these two capabilities. We showcase the state-of-the-art on isolated attosecond soft x-ray pulses for x-ray absorption near-edge spectroscopy to observe the 3d-state dynamics of the semi-metal TiS2 with attosecond resolution at the Ti L-edge (460 eV). We describe how the element- and state-specificity at the transition metal L-edge of the quantum material allows us to unambiguously identify how and where the optical field influences charge carriers. This precision elucidates that the Ti:3d conduction band states are efficiently photo-doped to a density of 1.9 × 1021 cm−3. The light-field induces coherent motion of intra-band carriers across 38% of the first Brillouin zone. Lastly, we describe the prospects with such unambiguous real-time observation of carrier dynamics in specific bonding or anti-bonding states and speculate that such capability will bring unprecedented opportunities toward an engineered approach for designer materials with pre-defined properties and efficiency. Examples are composites of semiconductors and insulators like Si, Ge, SiO2, GaN, BN, and quantum materials like graphene, transition metal dichalcogens, or high-Tc superconductors like NbN or LaBaCuO. Exiting are prospects to scrutinize canonical questions in multi-body physics, such as whether the electrons or lattice trigger phase transitions.
Congratulations to Emma for her first paper in the group!
Our paper appeared in Applied Physics Reviews and was selected as AIP featured article:
In addition a more accessible AIP SciLight appeared for this article:
A joint research project with the Bediako Group will receive $1M funding by the W. M. Keck Foundation to study novel 2D supercrystals and their magnetic properties at and far from equilibrium.
We are excited to welcome Richard Hollinger as post-doc to the Zuerch Lab! Richard completed his PhD at the Friedrich Schiller University and was awarded a Feodor Lynen Fellowship of the Alexander von Humboldt Foundation for his post-doc stay.
We are very excited to receive our first major grant funded by the Office of the President of the University of California within the Multicampus Research Programs and Initiative (MRPI). For the next 2 years, Michael will lead a team of researchers across the University of California to study the chemistry of liquids and solids on burried interfaces.
Here is the lay abstract for the project:
The world around us is governed by constant exchange of energy and particles. The internal structure at the interface between two media determines how phases interchange, how charge carriers exchange, and how media bind to one another. Therefore, understanding interfacial chemistry at a molecular level is of striking importance for a wide array of current challenges, such as clean water production, carbon dioxide capture, removal of plastics from water, clean energy production by photocatalysis, and energy storage in next generation solid-state batteries. Despite the importance, little is known about interfacial electronic and molecular structures, their dynamics, and how these lead to observed macroscopic properties and behaviors. The overarching goal of the California Interfacial Science Initiative (CISI) is to coordinate currently separate theoretical and experimental efforts studying interfaces across the University of California and leverage the combined expertise towards the creation of a world-leading center for interfacial science. During the pilot phase, multidisciplinary investigations will focus on two main topics: exploiting novel colliding planar liquid jets to study liquid-liquid interfaces investigating interfacial molecular dynamics relevant to CO2 capture and particle binding, and ionic charge transfer at solid-solid interfaces relevant to development of next generation batteries. The expertise for interfacial studies stems from first experiments on novel nonlinear X-ray spectroscopy that showed interfacial selectivity (UCB, LBNL) and a theory framework for nonlinear light-matter interactions (UCSD). CISI will bring together and consolidate these efforts by involving molecular level energy transfer theory (UCSC), interfacial engineering (UC-Merced) and quantum statistics calculation (LLNL). The multidisciplinary research team in the initiative will jointly develop advanced experimental techniques that enable studying these complex interfaces, which includes novel planar liquid jet technology, nonlinear optical and X-ray spectroscopies, and numerical models to simulate and understand interfacial dynamics.
The generation of high order harmonics from femtosecond mid-IR laser pulses in ZnO has shown great potential to reveal new insight into the ultrafast electron dynamics on a few femtosecond timescale. In this collaborative work between groups from Jena University, TU Vienna and UC Berkeley, we report on the experimental investigation of photoluminescence and high-order harmonic generation (HHG) in a ZnO single crystal and polycrystalline thin film irradiated with intense femtosecond mid-IR laser pulses. The ellipticity dependence of the HHG process is experimentally studied up to the 17th harmonic order for various driving laser wavelengths in the spectral range 3–4 µm. Interband Zener tunneling is found to exhibit a significant excitation efficiency drop for circularly polarized strong-field pump pulses. For higher harmonics with energies larger than the bandgap, the measured ellipticity dependence can be quantitatively described by numerical simulations based on the density matrix equations. The ellipticity dependence of the below and above ZnO band gap harmonics as a function of the laser wavelength provides an efficient method for distinguishing the dominant HHG mechanism for different harmonic orders.
Our paper appeared in Nanomaterials:
From fusion dynamics in stars, to terrestrial lightning events, to new prospects of energy production or novel light sources, hot dense plasmas are of importance for an array of physical phenomena. Due to a plethora of correlations in highly excited matter, direct probing of isolated dynamics remains challenging. Here, the 32.8-nm emission of a high-harmonic seeded laser-plasma amplifier (LPA), using eight-fold ionized Krypton as gain medium, is ptychographically imaged in longitudinal direction in the extreme ultraviolet (XUV). In excellent agreement with ab initio spatio-temporal Maxwell-Bloch simulations, an overionization of krypton due to nonlinear laser-plasma interactions is observed. This constitutes the first experimental observation of the laser ion abundance reshaping a laser plasma amplifier. The findings have direct implications for upscaling plasma-based XUV and X-ray sources and allow modeling light-plasma interactions in extreme conditions, similar to those of the early times of the universe, with direct experimental verification.
Our paper appeared in Nature’s Light: Science & Applications:
The photo shows PhD students Frederik and Tobias from the Spielmann Group at Jena University with the experimental apparatus used for the experiments. The chambers and a bit older version were built by Michael back during his own PhD.
We extend a warm welcome to Lars Hoffmann who joins our lab this Fall as joint graduate student with the Gessner Group. Lars received his Masters degree from the Free University in Berlin and worked with Michael at the Fritz Haber Institute in Berlin for is M.Sc. thesis before coming to Berkeley. Lars will work on gas phase dynamics in molecules in the Gessner Lab at the Lawrence Berkeley National Laboratory.
We are excited that Bailey Nebgen joins our lab this Fall as graduate student. She received her undergraduate degree from the University of Minnesota. Bailey will join our efforts on attosecond spectroscopy on quantum materials and THz spectroscopy.
Check out our newest preprint on investigating inversion-breaking symmetry in a polar metal lithium osmate using nonlinear X-ray spectroscopy!
Ferroelectric materials containing a switchable spontaneous polarization in combination with metallicity, hence polar metals, have intriguing prospects for exotic quantum phenomena such as unconventional pairing mechanisms giving rise to superconductivity, topological spin currents, anisotropic upper critical fields, Mott multiferroics, and the wide range of applications arising from these phenomena. Our experimental approach using element-specific nonlinear X-ray spectroscopy provides direct access to the symmetry breaking properties exerted by the lithium atom in the unit cell and enables mapping of the dielectric environment. We also perform ab initio density functional perturbation theory (DFPT) calculations to understand the implications of our experimental finding and to validate our observation.
In collaboration with UC San Diego, Lawrence Berkeley National Lab, the Pennsylvania State University and Argonne National Lab. Measurements performed at the SPring-8 Angstrom Compact free electron LAser (SACLA).
Link to Arxiv manuscript:
Our newest pre-print is out! In this work we demonstrate for the first time that we can perform second harmonic generation in the extreme ultraviolet at the titannium M-edge with a table-top instrument. This provides a new much more accessible route towards spectroscopy of surfaces and interfaces with elemental specificity. Emma’s first shared-first author paper in collaboration with the group of Tod Pascal at UCSD.
Link to the Arxiv manuscript:
Just published in Optics Letters. In this collaborative work together with the Eilenberger group at Jena University, we demonstrate a discrete dispersion scan scheme using a low number of flat windows to vary the dispersion of laser pulses in discrete steps. Monte Carlo simulations indicate that the pulse duration can be retrieved accurately with less than 10 dispersion steps, which we verify experimentally by measuring few-cycle pulses and material dispersion curves at 3 and 10 µm wavelength. This minimal measuring scheme using only five optical components without the need for linear positioners and interferometric alignment can be readily implemented in many wavelength ranges and situations.
Original link to the manuscript:
We are excited to welcome Alfred Zong as post-doctoral researcher to our group. Alfred did his undergraduate studies at Stanford and his PhD at the MIT. He is supported by the prestigous Miller Postdoctoral Fellowship. Alfred will join us studying fastest processes in correlated materials using attosecond diffraction spectroscopy.
We extend a warm welcome to our newest member Clarisse. She is an NSF REU undergraduate scholar at the University of Florida. Clarisse also enjoys synchronized swimming, painting, and hiking. We hope you enjoy the Bay!
Charge transport processes at interfaces which are governed by complex interfacial electronic structure play a crucial role in catalytic reactions, energy storage, photovoltaics, and many biological processes. Here, the first soft X-ray second harmonic generation (SXR-SHG)interfacial spectrum of a buried interface (boron/Parylene-N)is reported. SXR-SHG shows distinct spectral features that are not observed in X-ray absorption spectra, demonstrating its extraordinary interfacial sensitivity. Comparison to electronic structure calculations indicates a boron-organic separation distance of 1.9±0.1 Å, wherein changes as small as 0.1 Å result in easily detectable SXR-SHG spectral shifts (ca. 100s of meV). As SXR-SHG is inherently ultrafast and sensitive to individual atomic layers, it creates the possibility to study a variety of interfacial processes, e.g. catalysis, with ultrafast time resolution and bond specificity.
Original link to the pre-print:
Excitation of ionic solids with extreme ultraviolet pulses creates localized core-excitons, which in some cases couple strongly to the lattice. Here, core-excitonic states of magnesium oxide are studied in the time domain at the Mg L2,3edge with attosecond transient reflectivity spectroscopy.Attosecond pulses trigger the excitation of these short-lived quasi particles, whose decay is perturbed by time-delayed near infrared optical pulses. Combined with a few-state theoretical model, this reveals that the optical pulse shifts the energy of bright core-exciton states as well as induces featuresarising from dark core-excitons. We report coherence lifetimes for the first two core-excitons of 2.3±0.2 and 1.6±0.5 femtoseconds and show that these short lifetimes are primarily a consequence of strong exciton-phonon coupling, disclosing the drastic influence of structural effects in this ultrafast relaxation process.
Original link to the pre-print:
The complex-valued index of refraction of germanium in the extreme ultraviolet (XUV) is measured by multi-angle reflectance of synchrotron radiation. The resulting index of refraction is higher resolution than previously measured values. It reveals new structures attributed to transitions from the 3d-core orbitals to the Σ𝑐5,2 and the 𝑋𝑐5,2 conduction bands. Additionally, it is shown that the problem of total external reflection, which renders multi-angle reflectance measurements insensitive to the complex-valued refractive index at grazing incidence, can be overcome by employing measurements at angles of incidence away from the critical angle.
Original link to the journal:
Our recent book chapter, “Ptychography and Single-Shot Nanoscale Imaging with Plasma-Based Laser Sources” has been published in the International Conference on X-ray Lasers (Springer, 2020). We report the direct wavefront characterization of an intense ultrafast high-harmonic seeded soft X-ray laser at 32.8 nm wavelength and monitor the exit of the laser plasma amplifier depending on the arrival time of the seed pulses with respect to pump pulses.For the wavefront measurement in phase and intensity, we used high-resolution ptychography. After propagating the wavefront back to the source, we are able to observe the rear end of the plasma amplifier. We compare the characteristics of the seeded soft X-ray Laser to an unseeded one and find an increasing beam stability and lateral coherence important for lens less imaging techniques.
Original link to the Chapter:
! Our lab member, Angelique, had the opportunity to collect SHG data(see Research) at Japan’s X-ray Free Electron Laser (XFEL) SACLA. Big thank you to all of our collaborators and experimental team!
The crew at Jupiter’s!
Angelique, Diego, Emma and Can joined the group. The Zürch Force has assembled!
We are delighted to report that our ultrafast laser system arrived today in no less than 17 boxes. Many thanks to our effortless helpers on campus and the facility colleagues helping to get a temporary storage area prepared quickly. Quite some heavy lifting today, but totally worth it.
We welcome Ruoxu to our group as summer student. Ruoxu is starting her graduate research this Fall at Berkeley. She received her undergraduate degree from Grinnell College.
We are excited to announce that the Zuerch Lab is moving from the Fritz Haber Institute in Berlin, Germany, to the University of California at Berkeley following Michael accepting an offer to join the Faculty at Berkeley in the College of Chemistry as Assistant Professor. Our new labs are under construction in the D-levels of Giauque Hall and the offices in the neighbouring Hildebrand Hall on the Berkeley Campus.
Our paper “Retrieval of the complex-valued refractive index of germanium near the M4,5 absorption edge” has been published in the Journal of the Optical Society of America B. In this work we show that the complex-valued index of refraction of germanium in the extreme ultraviolet (XUV) is measured by multi- angle reflectance of synchrotron radiation. The resulting index of refraction is higher resolution than previously measured values. It reveals new structures attributed to transitions from the 3d-core orbitals to the Σ5c,2 and the X5c,2 conduction bands. Additionally, we show that the problem of total external reflection, which renders multi-angle reflectance measurements insensitive to the complex-valued refractive index at grazing incidence, can be overcome by employing measurements at angles of incidence away from the critical angle.
Original link to the journal:
Our paper “Wavelength-scale ptychographic coherent diffractive imaging using a high-order harmonic source”, which was the result of a collaboration between several Jena-based groups collaborating in a Forschergruppe in the State of Thuringia (2015 FGR 0094), has just been published in Scientific Reports. In this work, a full-field imaging resolution of 45 nm, corresponding to 2.5 wavelengths, was achieved using an advanced XUV source at the Institute of Applied Physics at FSU Jena. For better comparison of results in XUV imaging a Rayleigh-type criterion is used as a direct and unambiguous resolution metric for high-resolution table-top setup. This reliably qualifes this imaging system for real-world applications e.g. in biological sciences, material sciences, imaging integrated circuits and semiconductor mask inspection.
Original link to the journal:
Our perspective “Towards single shot time-resolved microscopy using short wavelength table-top light sources” has been published in Structural Dynamics and was selected as featured publication. In this perspective, we present the current state of the art techniques for full-field imaging in the extreme-ultraviolet- and soft X-ray-regime which are suitable for single exposure applications as they are paramount for studying dynamics in nanoscale systems. We evaluate the performance of currently available table-top sources, with special emphasis on applications, photon flux, and coherence. Examples for applications of single shot imaging in physics, biology, and industrial applications are discussed.
Original link to the journal:
Our paper on “Differentiating Photoexcited Carrier and Phonon Dynamics in the Δ, L, and Γ Valleys of Si(100) with Transient Extreme Ultraviolet Spectroscopy” has just been published by The Journal of Physical Chemistry. In this study, we prepared carrier populations in specific valleys in the band structure of silicon by tuning our narrow-band pump pulses in on the corresponding transition energies. We observe this specific excitation does not readily 1:1 imprint on the dynamics at the absorption edge. Using a BSE-DFT model, we find that besides the carrier population itself, contributions by excited phonon modes cause a perturbation of the core-hole transition probability that additionally modifies the observed transient XUV spectra.
Original link to the journal: